The study's first aim is to investigate the development of regular and problem substance use and abuse among youth in the context of other problem behaviors, including delinquency, mental health problems, and high risk sexual behaviors. The second aims is to investigate the development of these problem behaviors as a function of risk and protective factors. The study sample consists of 503 African-American and Caucasian boys in the youngest sample of the Pittsburgh Youth Study, who were first studied at ages 6-7, and who have been followed up over 13 assessments over the past nine years without interruption (up to ages 15- 16). The present proposal extends this follow-up with five yearly assessments until age 20. Since substance use, delinquency, mental health problems, and high risk sexual behaviors tend to become more serious during late adolescence, the study will be able to throw light on the relationships between the four problem domains in order to account for multi-problem youth that emerge during that period. Four developmental types of substance abuse are proposed and will be tested, an Early Onset Mixed Type, a Late Onset Delinquent Type, an Internalizing Type, and a Nondeviant History Type. The study is strengthened by the fact that risk and protective factors have already been measured over 12 data waves (in such domains as individual, family, peer, school, and neighborhood) and, together with the planned five data waves, will offer an unique opportunity to explain substance abuse and its co-occurring problems. In addition, the study is enriched by the collection of psychiatric diagnosis at age 7, 15, 18, 20 (with substance abuse and dependence diagnoses measured at all five proposed assessments), and biological data collected at age 15-16, which will allow an examination of the interaction between biological and social factors in the explanation of substance abuse and associated problems.